How to convert an object transformed by a Hook Modifier to an object with Loc,Rot,Scal Transformations?
You can parent both your object and the hooks to an empty, that would take care of the origin. 
You can also use the empty if you want to animate all the cubes relative to each other. 

However:
I would strongly suggest you just use an armature with 3 bones and put one vertex to weight 1, and the other 2 to 0 for each according bone. Hooks are dangerous, they have no rest position, and an armature keeps everything neat and tidy.

You'll probably need to check a more detailed tutorial on this, but here is the breakdown:
Add -> Armature
In edit mode on your triangle, select one of the vertices -> cursor to selected.
In edit mode on armature press SHIFT A, it will create a bone at the cursor location. Call the bone 'A', repeat for 2 other verts.
Object mode, select object, then armature -> CTRL P -> with empty groups.
Edit mode on your plane select a vertex, select the group of the bone it's supposed to be dragged by make sure weight is at 1.0 and press assign. 
Take One of your cubes, SHIFT-select the armature, go into pose mode, select the corresponding bone, CTRL P -> active bone, repeat. 
If this was too abstract there's tons of tutorials on that online.